A two-dimensional, high-resolution, non-linear, two-layer, free-surface, boundary-fitted co-ordinate, hydrostatic model was applied to study the time-space variability of hydraulic controls and the development of internal bores in the Strait of Gibraltar. The model predicts the occurrence of four averaged (over a tropical month) controls located to the west of the Spartel Sill, at the Spartel and Camarinal Sills and in the Tarifa Narrows. The last of these controls is apparent in the sense that it consists of discrete fragments alternating with subcritical flow regions. The only control which extends over the whole width of the strait is the control at the Camarinal Sill, but it breaks down during neap tide, too. This control exists concurrently with the control in the Tarifa Narrows for short periods, while for much of the tropical month there is either just one or neither of the controls. The model predicts the development of a hydraulic jump and a jump-drop pair near the Camarinal Sill; the appearance of bulges of Mediterranean water to the east and west of the sill; the large-amplitude and small-amplitude internal bores released from the Camarinal Sill, which travel, respectively, eastward and westward, and their transformation due to radial spreading and dissipative effects. Also presented here are the results illustrating the effects of earth's rotation on the internal bores in the Strait of Gibraltar. © 2001 Academic Press.